In the field of tire grooving and regrooving as well as the cutting of other heat sensitive material such as rubber or plastic belts or bands and the like, blades heated by electricity passing through the resistance of the blade have encountered substantial difficulty with blades heating in areas where the blade is not in the heat sensitive material and accordingly overheating. Further, significant heating is not provided where it is needed. For example, U.S. Pat. No. 4,539,467 to Wenger discloses an electrically heated cutting tool wherein a first limb of the blade is reduced in cross-sectional area at the bend to increase the production and concentration of heat in the cutting region to counteract the increased heat dissipation in the cutting region caused by the accumulation of excised material. Wenger requires and discloses a cooling device in the form of a cooling air supply provided in the handle for cooling parts of the blade away from the cutting region.
Further, in this field since there is a substantial amount of electricity required for the electrical resistance heating, the power supply and transformer are large and heavy requiring a separate power supply unit which is then connected to the cutting head by large heavy cables. This proved to be cumbersome in moving large heavy cables around as well as being tied to the power supply which must necessarily be located nearby. For example, U.S. Pat. No. 4,797,999 to Van Alstine discloses in Column 8 that the typical current required in a prior art resistance heated tire groover may be in the range of 50 amperes to 120 amperes. Wenger does not disclose shaping of a blade to produce an electrical resistance which reduces the current requirements enabling the entire unit including the power supply to be incorporated into the hand held unit.
Further, in the prior art the installation or changing of the blade proved to be a cumbersome process and the clamping of the blades to the cutting instrument often distorted the blades such that the blade legs were not aligned with the direction of cutting. For example, see U.S. Pat. No. 2,896,059 to Ruff discloses a mounting head assembly for an electrically heated cutting tool wherein the blades are mounted in grooves in a movable supporting block which rotates somewhat upon tightening of screws resulting in twisting the blade arms resulting in the blade arms not being aligned with the direction of cutting. Further, since the blade arms need to be inserted into the grooves and the grooves are movable because they are formed in a movable supporting block, the mounting of new blades is made difficult. As is common in the prior art, the fact that the movable supporting block of Ruff is not held away from the face of the cutting head further makes it difficult to insert the blades. Still further, the mounting head assembly of Ruff, as is common in the prior art, requires that the ends of the blade mate with the ends of the slots, which is much like threading a needle, and particularly difficult since the slots are moving.